1. Field of the Invention
The present invention relates to a processing solution for use in a silver dye bleaching process and particularly to a one bath type silver dye bleaching and silver bleaching solution for simultaneously carrying out dye bleaching and silver bleaching.
2. Description of the Prior Art
The silver dye bleaching process which has been known hitherto comprises the following processing steps. Namely, a sensitive material prepared by adding a mono-, bis- or polyazo dye or an azoxy dye to a silver halide emulsion is applied to a support. This is exposed to light, developed using a common black-and-white developing solution and then fixed. It is then processed with a dye bleaching solution, by which the dye is bleached by reduction in proportion to an amount of silver formed in the layer. In this case, a large amount of metal silver remains in the layer. In order to completely rehalogenate the metal silver or to change it into a soluble salt, it is processed with a silver bleaching solution after carrying out the dye bleaching. It is then dipped in a fixing solution such as a hypo solution, whereby the silver is completely removed and a dye image is formed.
The dye bleaching solution used after black-and-white development in the silver dye bleach process, whereby the dye is bleached in proportion to the amount of silver formed, is a strong acid solution containing:
1. AN ACID: FOR EXAMPLE, A HYDROHALOGENIC ACID, SULFURIC ACID OR SULFAMIC ACID, ETC.,
2. A COMPOUND WHICH REDUCES THE ELECTRIC POTENTIAL OF SILVER BY FORMING A SALT OR A COMPLEX WITH SILVER; FOR EXAMPLE, POTASSIUM IODIDE, MONOIODOACETIC ACID OR THIOUREA, ETC.,
3. A BLEACHING CATALYST (SUCH IS NOT ALWAYS NECESSARILY ADDED TO THE DYE BLEACHING SOLUTION; IT MAY ALSO BE ADDED TO THE SENSITIVE MATERIAL); FOR EXAMPLE, AN AZINE TYPE COMPOUND SUCH AS QUINOXALINE OR A QUINONE TYPE COMPOUND SUCH AS NAPHTHOQUINONE, ETC. The mechanism of dye bleaching is complicated, but it is believed that the acid decomposes the azo bond of the dye by reduction by means of silver as a catalyst.
In prior art silver dye bleaching processes, the sensitive material was processed by the silver bleaching solution after being processed by the dye bleaching solution. In general, there are two kinds of silver bleaching steps. One is for rehalogenating metallic silver using a solution containing, for example, a cupric salt and hydrohalogenic acid, ferricyanide and potassium halife, or an EDTA iron salt, etc., and the other is for changing metallic silver into a soluble silver salt using a solution containing potassium bichromate and acetic acid. In the former case, the rehalogenated material is then fixed by dipping in a hypo solution to change it into a soluble silver salt, whereby complete bleaching is carried out. In the latter case, though the metal silver becames a soluble salt by silver bleaching, it is subjected to fixing by the hypo solution, whereby complete desilvering is carried out. In either case, the dye image should not be harmed.
The dye bleaching and the silver bleaching should each be carried out quantitatively. If the dye bleaching is carried out in areas where metallic silver is not existent or is carried out regardless of the amount of silver, a precise dye image cannot be obtained after the dye bleaching or stain is generated. Further, if the dye bleaching cannot be completely carried out, a dye image cannot be seen precisely and the brightness of the dye image may deteriorate.
As described above, prior art silver dye bleaching processes have the defect that long processing is required since the dye bleaching and the silver bleaching are carried out separately. Accordingly, many attempts have been made in order to carry out dye bleaching and silver bleaching in the same bath. However, the dye bleaching and the silver bleaching are carried out as a competitive reaction. If the silver bleaching proceeds faster than the dye bleaching, there may be the defect that each function negates the other, for example, silver is oxidized (it sometimes becomes soluble) to result in a deterioration of its ability as a catalyst for dye bleaching. This problem in the prior one bath silver dye bleaching solutions has not been sufficiently overcome.
Further, the dye bleaching solution and the silver bleaching solution each have a strong acidity, because of containing hydrohalogenic acid. However, the hydrohalogenic acid used for provide the desired acidity has the defect that it corrodes processing machines or the other instruments used in the dark room and is harmful to human teeth, since it is volatile and has a strong oxidation ability.